EntitySetTEntity Methods

Ensures that the entity with a specified EntityIdentifier
is not removed or replaced with a different entity with the same identifier before
a transaction is committed. If another transaction commits first and removes or replaces
the entity, the transaction will raise a TransactionConflictException
when it is committed. It is valid to call this method with an id
that is not present in the entity set. In that case, a TransactionConflictException
will be thrown if an entity with id is added to the entity set in
another transaction.

Ensures that the entity set does not change at all before the transaction is committed.
If another transaction commits first and makes any changes to the entity set at all,
this transaction will raise a TransactionConflictException when it
is committed.